In their book "Theory of sets" Bourbaki suggested a general theory of isomorphism.

(See also http://www.tau.ac.il/~corry/publications/articles/pdf/bourbaki-structures.pdf )

The example of an untransportable relation (i.e. formula) in the book involves 2 principal base sets.

Are there examples of untrasportable formulas when we allow only one principal base set?